System and method of acoustic doppler beamforming

ABSTRACT

A system and method for forming acoustic beams is disclosed. One embodiment is an acoustic system configured to generate a plurality of beams non-orthogonal to a transducer array simultaneously with a vertical acoustic beam orthogonal to the array. The acoustic system includes a plurality of transducer elements arranged to form a two-dimensional array and electrically connected into rows in a first dimension and columns in a second dimension.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to acoustic transducers and beamformersthat form simultaneous multiple beams in multiple planes.

2. Description of the Related Technology

Devices such as Acoustic Doppler Velocity Sensors (ADVS) are widely usedfor measurement of vertical profiles of water current measurements andfor earth and/or water referenced velocity measurement for vesselnavigation. Acoustic Doppler Current Profilers (ADCP) are used infreshwater environments such as rivers, lakes and estuaries, as well asin saltwater environments such as the ocean, for studying the effects ofcurrent velocities. The measurement of accurate current velocities isimportant in such diverse fields as weather prediction, biologicalstudies of nutrients, environmental studies of sewage dispersion, andcommercial exploration for natural resources, including oil.

Such devices measure 3-axis velocities by measuring velocity along linesof position defined by narrow acoustic beams. Three or more beamsoriented at different directions may be used to measure the threeorthogonal velocity components. Such devices may employ four narrow(e.g., 1° to 4°) conical transmit/receive beams are employed positionedin two axes of a plane surface and inclined relative to the normal tothat plane. In this configuration, which is referred to as a Janusconfiguration, two sets of narrow conical beams are symmetricallyinclined outward and positioned at four 90° circumferential incrementson the surface of a larger (typically 60°) outward opening cone. Marineinstrumentation is frequently used in environments that are sensitive toone or more of size, power consumption, and cost. Accordingly, a needexists for suitable methods and apparatuses for generating acousticbeams for use in ADVS and ADCP devices.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

The system, method, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention as expressed bythe claims which follow, its more prominent features will now bediscussed briefly. After considering this discussion, and particularlyafter reading the section entitled “Detailed Description of CertainEmbodiments” one will understand how the features of this inventionprovide advantages such as a compact, low complexity beam forming systemthat provides a vertical beam formed in the aperture of a twodimensional transducer array along with beams formed in at least twoother dimensions.

One embodiment includes an acoustic system. The acoustic system includesa plurality of transducer elements arranged to form a two-dimensionalarray and electrically connected into rows in a first dimension andcolumns in a second dimension. The acoustic system further includes atleast two first beamforming circuits configured to generate a pluralityof beams in at least two planes. Each of the beams defines anon-orthogonal angle with the transducer array. The acoustic systemfurther includes a second beamforming circuit connected to each of thebeamforming circuits and configured to generate a beam orthogonal to thetransducer array. Each of the first beamforming circuits is electricallyconnected to each of the transducer elements so that each of thetransducer elements contributes to each of the beams in the at least twoplanes.

One embodiment includes a system for generating a plurality of acousticbeams. The system includes means for generating a plurality of acousticsignals. The generating means includes a plurality of means forconverting between an electrical signal and a respective one of theacoustic signals. The converting means are arranged to form a twodimensional array and electrically connected into rows in a firstdimension and columns in a second dimension. The system further includesmeans for simultaneously forming a plurality of first beams in at leasttwo planes based on the acoustic signals. Each of the first beamsdefines a non-orthogonal angle with the transducer array and whereineach of the first beams is based on each of the respective plurality ofsignals of each of the converting means. The system further includesmeans for forming a second beam orthogonal to the array based on theacoustic signals. The first and second beams are formed simultaneously.

Another embodiment includes a method of generating a plurality ofacoustic beams. The method includes generating a plurality of acousticsignals in each of a plurality of transducer elements arranged to form atwo dimensional array and electrically connected into rows in a firstdimension and columns in a second dimension. The method further includessimultaneously forming a plurality of first beams in at least two planesbased on the acoustic signals. Each of the first beams defines anon-orthogonal angle with the transducer array and wherein each of thefirst beams is based on each of the respective plurality of signals ofeach of the transducer elements. The method further includes forming asecond beam orthogonal to the transducer array based on the acousticsignals. The first and second beams are formed simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a prior art 4-piston transducer array having aJanus configuration.

FIG. 2 is a perspective view illustrating a configuration of fouracoustic beams inclined relative to one embodiment of a two dimensionaltransducer array.

FIG. 3 is a perspective view illustrating one embodiment of a twodimensional transducer array along with a configuration of four acousticbeams inclined relative to the array and a fifth beam normal to thearray.

FIG. 4 is a schematic diagram illustrating one embodiment of an acousticsystem configured to generate a plurality of inclined acoustic beams anda vertical acoustic beam of FIG. 3.

FIG. 5 is a schematic diagram illustrating in more detail one embodimentof the acoustic system illustrated in FIG. 4 when configured to receivethe beams.

FIG. 6 is a schematic diagram illustrating in more detail one embodimentof the acoustic system illustrated in FIG. 4 when configured to transmitthe beams.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different ways as defined and covered by the claims. Inthis description, reference is made to the drawings wherein like partsare designated with like numerals throughout.

ADVS and ADCP devices may include transducer and beamforming devices forgenerating the acoustic beams used to measure water velocities. Forexample, FIG. 1 is a top view of a prior art 4-piston transducer array100 in Janus configuration. Such a 4-piston Janus transducer assemblycomprises four independent circular piston-type transducers 102, eachproducing a single narrowly dispersed conical transmit/receive beamdirected normal to the piston face. The four transducers are physicallypositioned in a rigid assembly to direct the output of the transducers102 so as to generate the Janus beam configuration.

FIG. 2 is a perspective view illustrating a configuration of fouracoustic beams 210 inclined relative to one embodiment of a twodimensional transducer array 200. In the embodiment illustrated in FIG.2, the transducer array 200 comprises a two dimensional array oftransducer elements 202 configured to generate simultaneously generatethe beams 210. One embodiment of such a transducer array and a suitablebeamformer are disclosed in U.S. Pat. No. 5,808,967, which is herebyincorporated by reference in its entirety.

FIG. 3 is a perspective view illustrating one embodiment of a twodimensional transducer array 300 along with a configuration of fouracoustic beams 210 inclined relative to the array and a fifth beam 212normal to the array. In some applications, it is desirable to add theadditional vertical beam 212 to the two dimensional beams 210. Forexample, such an additional beam 212 is useful for wave measurements,echo sounder measurements, Reynolds stress measurements, Dopplervelocity measurements, and bathymetry. The fifth vertical beam 210 alsoallows Doppler velocity measurements even at extreme tilt angles,without gimballing of the transducer. Moreover, as noted above, marineinstrumentation is frequently used in environments that are sensitive toone or more of size, power consumption, and cost. Accordingly, in oneembodiment, the system 300 includes a low (added) complexity beamformerusing a phased array of transducers 202 to generate the vertical beam212 in addition to other, e.g., Janus, beams 210. In one embodiment, thevertical beam 212 can be formed in a single aperture along with theother beams.

FIG. 4 is a schematic diagram illustrating one embodiment of an acousticsystem 400 that is configured to generate a plurality of inclinedacoustic beams 210 and a vertical acoustic beam 212 using the transducerarray 300 of FIG. 3. The coordinate system used for the purposes of thisdescription is as shown with rows 306 oriented in the X axis, columns304 in the Y axis, and the Z axis normal to the plane face 316. Thetransducer elements 202 are electrically interconnected along columns(“Y”) 304 (and collectively identified as “Y” connections 305) and rows306 (and collectively identified as “X” connections 307). The “X”connections 307 are connected to an “X” transmit beamformer 402 and an“X” receive beamformer 404 via a transmit/receive switch 406. The “Y”connections 305 are connected to a “Y” transmit beamformer 412 and a “Y”receive beamformer 414 via a transmit/receive switch 416. The transmitbeamformers 402 and 412 and receive beamformers 404 and 414 may beeither phase or time-delay beamforming networks. In one embodiment, acommon mode connection connects a vertical transmit beamformer 422 avertical receive beamformer 424 to the “X” connections 307 and the “Y”connections 305 via a transmit/receive switch 424. It has been foundthat such a common mode connection provides a simple and compact way ofconnecting the vertical beamformers 422 and 424 to the array 300. In onembodiment, the rows 306 are connected on the back sides (not shown) ofeach transducer element 202 and the columns 304 are connected to thefront sides (e.g., along the face 316) of each transducer 202.

Any suitable beamformer may be used, including the beamformers disclosedin the above incorporation U.S. Pat. No. 5,808,967. Each of thebeamformers 402, 412, 422, 404, 414, and 424 may comprise suitableamplifiers and receivers for processing transmitted and receivedsignals. The beamformers 402, 412, 422, 404, 414, and 424 may be furtherconnected to one or more processors configured to process the signals.

In one embodiment, the array 300 is formed from several cylindricaldiscs (each having a diameter about equal to that of the final array),which are sequentially bonded together and partially sliced with aparallel diamond blade saw at various stages of the process such thatthe sliced elements are rigidly held together by a solid layer. Whencompleted, the array 300 is internally diced into the desired form withthe suitable precision, and held in shape by the combination of amechanically rigid and acoustically transparent front facing and a solidbacking disc.

In the illustrated array 300 of FIG. 4, the array face 316 defines asubstantially circular shape. However, other form factors such asellipses or polygons, which are generally symmetrical in the two facedimensions, are also suitable for forming narrow inclined beams ofgeneral conical form. Each of the transducer elements 202 havesubstantially symmetrical faces that define circular, or rectangularforms (i.e., in their facial cross-section). The face width of eachelement is approximately 0.5λ, where λ is the acoustic wavelength inwater of the desired center frequency. For example, to form beams with4° beam width, an array diameter of approximately 16λ is desirable,comprising a 32×32 element array of approximately 800 elements. The backside rows 306 (X direction) and front side columns 304 (Y direction) ofthe array elements 202 are electrically connected together alongparallel lines of elements with acoustically transparent material. Therows and columns may be orthogonal to each other.

FIG. 5 is a schematic diagram illustrating in more detail one embodimentof the acoustic system 400 when configured to receive the beams 210 and212. It is to be recognized that while a 4×4 array is illustrated,arrays may have any suitable number of elements 202, e.g., 32×32 arraysof elements 202.

The spacing of the elements 202 is determined by reference to thedesired operating parameters. For example, during receipt of a long toneburst acoustic signal at a single frequency (narrowband), f, withwavelength, λ=c/f, where c is the sound propagation velocity in thefluid media, incoming sound wavefronts traveling in the negative Xdirection and at an angle θ with the Z axis (Z being normal to the arrayplane, or normal to the plane of the Figure) travel different distancesto each of the Y-axis (frontside) column line-arrays 304, and thusstrike each of the line arrays at different times, and in general, withdifferent phases. The path length differences 506, α, between adjacentline-arrays is related to the element center-to-center separationdistance (d) by α=d sin θ. The wavefront arrival time differencesbetween adjacent line-arrays is τ=α/c=(d//c)sin θ. If the elements arespaced at distances corresponding to a half-wavelength of the arrivingnarrowband signal (d=λ/2), the path length difference expressed in termsof arriving signal wavelengths is given by α=(λ/2)sin θ. For an arrivalangle of 30°, α(λ/2)sin 30°=λ/4, which corresponds to an inter-elementangular phase shift of 90° for arriving narrowband signals. Thus, when anarrowband pulse is being received by all Y-axis line-arrays with thebackside coupled to virtual grounds, the received electrical signalphases along the set of four Y-axis line-arrays will be 0, 90, 180, and270 degrees, respectively.

Each of the rows 304 and columns 306 is configured to be phase shiftedfrom each adjacent row 304 or column 306. For example, in theillustrated embodiment, each row 304 and column 306 is phase shifted by90° from each adjacent row 304 or column 306. The “X” transmit/receiveswitch 406 is connected to a pair of transformers 500 that are eachconnected across pairs of the columns 306 that are shifted 180° inphase. For example, connected to the “X” transmit/receive switch 406 isone transformer 500 connected across the columns 306 shifted by 0° and180° relative to the transducer column 306 closest to the Y axis andanother transformer 500 is connected across the columns 306 shifted by90° and 270° to the transducer column 306 closest to the Y axis.Similarly, connected to the “Y” transmit/receive switch 406 is onetransformer 500 connected across the rows 304 shifted by 0° and 180°relative to the transducer rows 304 closest to the X axis and anothertransformer 500 is connected across the rows 304 shifted by 90° and 270°to the transducer row 304 closest to the X axis.

A transformer 502 is connected to center taps of each of thetransformers 500 and to the vertical beamformers 422 and 424 via theswitch 426. In particular, the transformer 502 connects the center tapsof the transformers 500 that connect to the rows 304 with the centertaps of the transformers 500 that connect to the columns 306. Thisconnection of the transformer 502 creates a common mode connectionbetween the rows and columns.

In one embodiment, the vertical beamformers 422 and 424 are connected toeach of the transducer elements 202. Thus, in such an embodiment, thevertical beam 212 has an aperture that is greater than thenon-orthogonal beams 210 by 1/cos (beam angle). Where a wider verticalbeam 212 is desired, less than all of the rows and columns is connectedto the vertical beamformers 422 and 424 to create a smaller aperturearray for the vertical beam 212. For example, the aperture of thevertical beam 102 may be reduced to reduce sensitivity to tilt of thearray 300. In one such embodiment, a group of rows and columns in acentral region of the array 300 is connected to the vertical beamformers422 and 424 to create the “sub-array” for forming the vertical beam 212.

While only a 4×4 section of the array 300 is illustrated, it is to berecognized that the rows 306 and columns 304 of an array 300 larger than4×4 may also be constructed in which the four signal phases are repeatedin additional 4×4 sets of rows and columns. For example, a 32×32 arraymay comprise 8 repeating sets of the 4 illustrated rows 306 having phaseshifts of 0°, 90°, 180°, and 270° and 8 repeating sets of the fourillustrated columns 304 having phase shifts of 0°, 90°, 180°, and 270°.The rows 306 and columns 304 with each particular phase shift are summedand connected in parallel to the corresponding transformer 500 (e.g.,each input of the transformer 500 is connected to 8 rows or 8 columns inparallel). Each 4×4 increase in size of the array 300 further enhancesthe interference patterns at ±30°. When additional sets of such fourline-array segments are utilized as described, the acoustic signal gainalong the ±30° directions is increased, or correspondingly, thebeamwidth in that direction is reduced, as additional such sets ofarrays are added.

In receive operation, acoustic signals are converted to electricalsignals by the transducer elements 202 and received by the beamformers404, 414, and 424. The “X” and “Y” beamformers 404 and 414simultaneously form non-orthogonal beams 210 in at least two planes suchas the Janus beams of FIG. 3 while the vertical beamformer 424simultaneously forms the vertical beam 212. Each set of four X-axiselectrical signals (rows 306 or columns 304) are connected to virtualground nodes (not shown) in the receiver preamplifier of the receivebeamformers 404 and 414 to form a signal reference for the backsiderows, and phase shifted −90° between adjacent line-arrays (0°, −90,−180°, and −270°), as shown. The phase shifts compensate for thosearising from the different inter-element path lengths of the acousticpulse incident on the line arrays. The resulting four signals of therows 306 and the signals of the columns 304 will be in phase and, whensummed, will form a maximum acoustic interference pattern when receivinga wavefront arriving at a about a 30° incidence angle. This maximumcorresponds to the central axis of one of the main lobes of the formedbeams. A second receive beam can be formed for incoming acousticwavefronts traveling in the negative X direction and at an angle θ withthe Z direction (at a −30° incidence angle) by reversing the sign of the90° imposed phase shift on the four signals and summing the signals.Because each of the beamformers 402, 404, 412, and 414 are connected toeach of the transducer elements 202, each of the non-orthogonal beams210 includes a contribution from each of the transducer elements 202.

The vertical beamformer 424 simultaneously generates the vertical beam212 by driving the rows 306 and columns 304 180° apart using thetransformer 502. Driving the rows 306 and columns 304 in this waymatches the ½ wavelength distance, d, between each row and column.

FIG. 6 is a schematic diagram illustrating in more detail one embodimentof the acoustic system 400 when configured to transmit the beams 210 and212. Transmit operation is substantially similar to receive operationdescribed above, except that electrical signals generated by thebeamformers 402, 412, and 422 are converted to acoustic signals by thetransducer elements 202.

In view of the above, one will appreciate that the invention overcomesthe problem of creating a vertical beam in acoustic marine instruments.For example, one embodiment includes a compact, low complexity beamforming system that provides a vertical beam formed in the aperture of atwo dimensional transducer array along with beams formed in at least twoother dimensions.

It is to be recognized that depending on the embodiment, certain acts orevents of any of the methods described herein can be performed in adifferent sequence, may be added, merged, or left out all together(e.g., not all described acts or events are necessary for the practiceof the method). Moreover, in certain embodiments, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

Those of skill will recognize that the various illustrative logicalblocks, modules, circuits, and algorithm steps described in connectionwith the embodiments disclosed herein may be implemented as electronichardware, computer software, or combinations of both. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

While the above detailed description has shown, described, and pointedout novel features of the invention as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the spirit of theinvention. As will be recognized, the present invention may be embodiedwithin a form that does not provide all of the features and benefits setforth herein, as some features may be used or practiced separately fromothers. The scope of the invention is indicated by the appended claimsrather than by the foregoing description. All changes which come withinthe meaning and range of equivalency of the claims are to be embracedwithin their scope.

What is claimed is:
 1. An acoustic system, comprising: a plurality oftransducer elements arranged to form a two-dimensional array andelectrically connected into rows in a first dimension and columns in asecond dimension; at least two first beamforming circuits configured togenerate a plurality of beams in at least two planes, each of the beamsdefining a non-orthogonal angle with the transducer array; and a secondbeamforming circuit electrically connected to each of the firstbeamforming circuits and configured to generate a beam orthogonal to thetransducer array, wherein each of the first beamforming circuits iselectrically connected to each of the transducer elements so that eachof the transducer elements contributes to each of the beams in the atleast two planes.
 2. The system of claim 1, wherein the plurality ofbeams comprises a Janus configuration that is formed simultaneously withthe vertical beam.
 3. The system of claim 1, wherein the secondbeamforming circuit comprises a common mode electrical connection toeach of the first beamforming circuits.
 4. The system of claim 1,wherein each of the first beamforming circuits are connected to avirtual ground node for all rows and columns.
 5. The system of claim 4,wherein each of the first beamforming circuits is connected to thetransducer array via a respective transformer.
 6. The system of claim 5,wherein the second beamforming circuit comprises a second transformerconnected to the center tap of each of the respective transformers ofeach of the first beamforming circuits.
 7. The system of claim 6,wherein the second transformer provides a common mode electricalconnection to the respective transformers of each of the firstbeamforming circuits.
 8. The system of claim 1, wherein the secondbeamforming circuit is connected to less than all of the transducerelements.
 9. The system of claim 8, wherein the less than all of thetransducer elements are adjacent to each other and positionedsubstantially in the center of the array of transducer elements.
 10. Thesystem of claim 1, wherein the second beamforming circuit is connectedto each of the transducer elements.
 11. The system of claim 1, whereinthe first beamforming circuits are configured to phase shift signals inadjacent rows and columns of the transducer elements.
 12. A system forgenerating a plurality of acoustic beams, the system comprising: meansfor generating a plurality of acoustic signals, the means comprising aplurality of means for converting between an electrical signal and arespective one of the acoustic signals, wherein the converting means arearranged to form a two dimensional array and electrically connected intorows in a first dimension and columns in a second dimension; means forsimultaneously forming a plurality of first beams in at least two planesbased on the acoustic signals, each of the first beams defining anon-orthogonal angle with the transducer array and wherein each of thefirst beams is based on each of the respective plurality of signals ofeach of the converting means; and means for forming a second beamorthogonal to the array based on the acoustic signals, wherein the firstand second beams are formed simultaneously.
 13. The system of claim 12,wherein the plurality of beams comprises a Janus configuration that isformed simultaneously with the vertical beam.
 14. The system of claim12, wherein the means for forming the second beams comprises a commonmode electrical connection to means for forming the first beams.
 15. Thesystem of claim 12, wherein each of the means for forming the firstbeams are connected to a virtual ground node for all rows and columns.16. The system of claim 15, wherein the means for forming the firstbeams comprises at least two beamforming circuits and where each of thefirst beamforming circuits is connected to the transducer array via arespective transformer.
 17. The system of claim 16 wherein the means forforming the second beam comprises a second beamforming circuit, andwherein the second beamforming circuit comprises a second transformerconnected to the center tap of each of the respective transformers ofeach of the first beamforming circuits.
 18. The system of claim 17,wherein the second transformer provides a common mode electricalconnection to the respective transformers of each of the firstbeamforming circuits.
 19. The system of claim 12, wherein means forforming the second beam is connected to less than all of the convertingmeans.
 20. The system of claim 19, wherein the less than all of thetransducer elements are adjacent to each other and positionedsubstantially in the center of the array of transducer elements.
 21. Thesystem of claim 12, wherein means for forming the second beam isconnected to each of the converting means.
 22. The system of claim 12,wherein means for forming the first beams are configured to phase shiftsignals in adjacent rows and columns of the converting means.
 23. Amethod of generating a plurality of acoustic beams, the methodcomprising: generating a plurality of acoustic signals in each of aplurality of transducer elements arranged to form a two dimensionalarray and electrically connected into rows in a first dimension andcolumns in a second dimension; simultaneously forming a plurality offirst beams in at least two planes based on the acoustic signals usingat least two first beamforming circuits, each of the first beamsdefining a non-orthogonal angle with the transducer array and whereineach of the first beams is based on each of the respective plurality ofsignals of each of the transducer elements; and forming a second beamorthogonal to the transducer array based on the acoustic signals using asecond beamforming circuit, wherein the first and second beams areformed simultaneously.
 24. The method of claim 23, wherein the pluralityof beams comprises a Janus configuration that is formed simultaneouslywith the vertical beam.
 25. The method of claim 23, wherein the secondbeam is formed based on the signals of less than all of the transducerelements.
 26. The method of claim 25, wherein the less than all of thetransducer elements are adjacent to each other and positionedsubstantially in the center of the array of transducer elements.
 27. Themethod of claim 23, further comprising phase shifting the acousticsignals adjacent one of the rows and columns of transducer elements. 28.The system of claim 1, further comprising controlling the aperture ofthe beam orthogonal to the transducer array by selecting at least onetransducer element, the selected at least one transducer elementcomprising less than all of the transducer elements.
 29. The method ofclaim 23, further comprising controlling the aperture of the beamorthogonal to the transducer array by selecting at least one transducerelement, the selected at least one transducer element comprising lessthan all of the transducer elements.
 30. An acoustic system, comprising:a plurality of transducer elements arranged to form a two-dimensionalarray and electrically connected into rows in a first dimension andcolumns in a second dimension; a first beamforming circuit configured togenerate a plurality of beams in at least two planes, each of the beamsdefining a non-orthogonal angle with the transducer array; and a secondbeamforming circuit electrically connected to the first beamformingcircuit and configured to generate a beam orthogonal to the transducerarray, wherein the first beamforming circuit is electrically connectedto each of the transducer elements so that each of the transducerelements contributes to each of the beams in the at least two planes.31. The system of claim 30, wherein the plurality of beams comprises aJanus configuration that is formed simultaneously with the verticalbeam.
 32. The system of claim 30, wherein the second beamforming circuitcomprises a common mode electrical connection to each of the firstbeamforming circuits.
 33. The system of claim 30, wherein the firstbeamforming circuit is connected to a virtual ground node for all rowsand columns.
 34. The system of claim 33, wherein the first beamformingcircuit is connected to the transducer array via a respectivetransformer.
 35. The system of claim 34, wherein the second beamformingcircuit comprises a second transformer connected to the center tap ofeach of the respective transformers of the first beamforming circuit.36. The system of claim 35, wherein the second transformer provides acommon mode electrical connection to the respective transformers of thefirst beamforming circuit.
 37. The system of claim 30, wherein thesecond beamforming circuit is connected to less than all of thetransducer elements.
 38. The system of claim 37, wherein the less thanall of the transducer elements are adjacent to each other and positionedsubstantially in the center of the array of transducer elements.
 39. Thesystem of claim 30, wherein the second beamforming circuit is connectedto each of the transducer elements.
 40. The system of claim 30, whereinthe first beamforming circuit is configured to phase shift signals inadjacent rows and columns of the transducer elements.
 41. A method ofgenerating a plurality of acoustic beams, the method comprising:generating a plurality of acoustic signals in each of a plurality oftransducer elements arranged to form a two dimensional array andelectrically connected into rows in a first dimension and columns in asecond dimension; simultaneously forming a plurality of first beams inat least two planes based on the acoustic signals using a firstbeamforming circuit, each of the first beams defining a non-orthogonalangle with the transducer array and wherein each of the first beams isbased on each of the respective plurality of signals of each of thetransducer elements; and forming a second beam orthogonal to thetransducer array based on the acoustic signals using a secondbeamforming circuit, wherein the first and second beams are formedsimultaneously.
 42. The method of claim 41, wherein the plurality ofbeams comprises a Janus configuration that is formed simultaneously withthe vertical beam.
 43. The method of claim 41, wherein the second beamis formed based on the signals of less than all of the transducerelements.
 44. The method of claim 43, wherein the less than all of thetransducer elements are adjacent to each other and positionedsubstantially in the center of the array of transducer elements.
 45. Themethod of claim 41, further comprising phase shifting the acousticsignals adjacent one of the rows and columns of transducer elements. 46.The system of claim 30, further comprising controlling the aperture ofthe beam orthogonal to the transducer array by selecting at least onetransducer element, the selected at least one transducer elementcomprising less than all of the transducer elements.
 47. The method ofclaim 41, further comprising controlling the aperture of the beamorthogonal to the transducer array by selecting at least one transducerelement, the selected at least one transducer element comprising lessthan all of the transducer elements.